Tracking of motion of a pointing device using a single buffer for cross and auto correlation determination

Cross correlation between a reference image frame and a comparison image frame determine the direction of motion relative to x and y orthogonal axes for a pointing device (42,60) that uses optical imaging to monitor movement relative to a surface (62). Pixel data for a portion of the surface are loaded into a buffer memory (122) that shifts the data between successive positions in the buffer memory as each pixel of a comparison frame is processed to compute cross correlation. Auto correlation is determined for positions in the reference frame and used with the cross correlation results to determine a sub-pixel interpolation for the movement of the pointing device. A new reference frame is loaded using data for the comparison frame currently being processed if the pointing device is moved sufficiently so that the next comparison frame will not overlap the existing reference frame.